Base Station Apparatus and Transmit Power Control Method

1. A base station apparatus comprising: a signal to interference ratio calculator that calculates a signal to interference ratio using a value obtained by averaging interference signal power for several slot times; a reference value decider that decides whether the calculated signal to interference ratio is greater than a reference value or not; and a transmit power control information creator that creates transmit power control information to instruct either an increase or decrease of transmit power based on the number of slots used to calculate the averaged interference signal power and the decision result of said reference value decider, wherein: when the number of slots used to calculate the averaged interference signal power equals or exceeds a predetermined number, the transmit power control information creator creates the transmit power control information based on the decision result of the reference value decider, and when the number of slots used to calculate the averaged interference signal power is less than the predetermined number, regardless of the decision result of the reference value decider, the transmit power control information creator creates the transmit power control information so as not to allow a transmit power level to fall below a predetermined level.

2. The base station apparatus according to claim 1 , wherein when the number of slots used to calculate the averaged interference signal power is less than the predetermined number, the transmit power control information creator creates the transmit power control information instructing an increase of the transmit power.

3. The base station apparatus according to claim 1 , wherein when the number of slots used to calculate the averaged interference signal power is less than the predetermined number, the transmit power control information creator creates the transmit power control information so that a count of transmit power control information instructing an increase of the transmit power created so far does not fall below a count of transmit power control information instructing a decrease of the transmit power.

4. The base station apparatus according to claim 1 , wherein when the number of slots used to calculate the averaged interference signal power is less than the predetermined number, the transmit power control information creator creates transmit power control information whose content is opposite to that of the immediately preceding transmit power control information.

5. The base station apparatus according to claim 1 , wherein when the number of slots used to calculate the averaged interference signal power equals or exceeds the predetermined number, the transmit power control information creator creates transmit power control information instructing a decrease of the transmit power when the signal to interference ratio is greater than the reference value and creates transmit power control information instructing an increase of the transmit power when the signal to interference ratio is equal to or smaller than the reference value.

6. The base station apparatus according to claim 1 , wherein the signal to interference ratio calculator starts to measure interference signal power for a communication terminal apparatus with which to establish a new radio connection prior to starting control of uplink transmit power of the communication terminal apparatus based on the transmit power control information that is inserted into the downlink.

7. A closed loop transmit power control method whereby a base station apparatus transmits transmit power control information to a communication terminal apparatus and the communication terminal apparatus sets transmit power based on the transmit power control information, the method comprising having the base station apparatus create transmit power control information instructing an increase of transmit power until the base station apparatus can correctly estimate interference signal power against a signal sent from a communication terminal apparatus with which a new radio connection has been established.

8. The transmit power control method according to claim 7 , wherein the base station apparatus starts to measure interference signal power in advance for the communication terminal apparatus with which to establish the new radio connection.

9. A closed loop transmit power control method whereby a base station apparatus transmits transmit power control information to a communication terminal apparatus and the communication terminal apparatus sets transmit power based on the transmit power control information, the method comprising having the base station apparatus create transmit power control information so that a count of the transmit power control information instructing an increase of transmit power created so far does not fall below a count of the transmit power control information instructing a decrease of transmit power, until the base station apparatus can correctly estimate interference signal power against a signal sent from a communication terminal apparatus with which a new radio connection has been established.

10. A closed loop transmit power control method whereby a base station apparatus transmits transmit power control information to a communication terminal apparatus and the communication terminal apparatus sets transmit power based on the transmit power control information, the method comprising having the base station apparatus create transmit power control information whose content is opposite to that of an immediately preceding transmit power control information, until the base station apparatus can correctly estimate interference signal power against a signal sent from a communication terminal apparatus with which a new radio connection has been established.